KR100632424B1 - Lithographic Apparatus and Device Manufacturing Method - Google Patents

Abstract

In the present invention, there is provided a substrate table WT for holding a substrate W, a projection system PL for projecting a patterned beam onto a target portion of the substrate W, and isolation for providing a reference plane on which the substrate is measured. There is provided a lithographic apparatus comprising a reference frame MF, wherein the reference frame MF comprises a material having a high coefficient of thermal expansion.

Description

Lithographic Apparatus and Device Manufacturing Method

1 is an illustration of a lithographic apparatus according to one embodiment of the invention;

2 is a detailed view of a lithographic apparatus according to a further embodiment of the present invention;

3 is a plan view of an isolated reference frame from a base frame in accordance with an embodiment of the present invention showing particular components supported on the reference frame;

4 is a bottom view of a reference frame isolated from the base frame as shown in FIG. 3;

5 is a detail view of the reference frame and projection lens and thermal conditioning system;

6 to 8 are diagrams showing the results obtained according to an embodiment of the present invention.

The present invention relates to a lithographic apparatus and a device manufacturing method.

BACKGROUND A lithographic apparatus is a machine that applies a necessary pattern onto a target portion of a substrate. Lithographic projection apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In this case, patterning means such as a mask can be used to create a circuit pattern corresponding to each layer of the IC, which pattern is a target on a substrate (e.g. a silicon wafer) having a layer of radiation sensitive material (resist). It may be imaged on a portion (eg, including part of one or several dies). In general, a single wafer includes a network of adjacent target portions that are successively exposed. A known lithographic apparatus scans a pattern through a projection beam in a given direction ("scanning" direction) with a so-called stepper through which each target portion is irradiated by exposing the entire pattern onto the target portion at once, And a so-called scanner to which each target portion is irradiated by synchronously scanning the substrate in the opposite direction or the opposite direction.

Lithographic apparatus include a frame of reference, also referred to in the art as a metrology frame. The frame of reference provides a support for the projection system. In certain forms of conventional lithographic apparatus, the reference frame is isolated from disturbances caused by other components of the lithographic apparatus, such as long stroke and single stroke motors used to drive the reticle and wafer stages. ). Reference frames are typically made of materials having a low coefficient of thermal expansion, such as a alloy containing Invar. Until now, it has been assumed that such low thermal expansion materials are necessary to meet the thermal requirements of the reference frame. Unfortunately, these materials are expensive due to high manufacturing costs. In addition, these materials have limited supply and limited manufacturability. In terms of active market action of supply and demand, these factors contribute to causing unacceptably long lead times in the manufacture of the reference frame. This long lead time involves a large expenditure in terms of the man hour required to construct the reference frame due to the sub-optimal manufacturability of conventional reference frame materials. Due to problems in the supply and demand of the reference frame, the output will not be able to supply a sufficiently high volume of support frames in an upturn, and the output will fall, and in the downtown, The product must be stored in the warehouse because it cannot be reduced.

US-A-6 529 264 discloses a frame connecting parts of an optical system, which includes two barrels arranged on top of their own flange-connection to the assembly frame. The patent addresses the problem that movements between certain points of a relatively weakly connected optical axis result in a loss of imaging performance. In particular, the patent addresses the problem associated with reducing such movements in the frame. It is apparent that the frame is made of materials including aluminum and stainless steel. The frame does not constitute a reference frame but is seen as part of the projection optical assembly, which serves to improve the imaging performance of the assembly. Thus, the patent points to a technical bias that frames for lithographic apparatus made of materials with a low coefficient of thermal expansion, such as aluminum, have a devastating effect on the performance of the lithographic apparatus and undergo vibrations that require additional solutions. The patent implies that the disclosed frame is not suitable as a reference frame because it undergoes vibration. In US-A-6 529 264, the additional solution required includes a method for providing an additional frame. Providing additional frames creates an overdetermined structure since a single small assembly frame is sufficient. In order to overcome the mechanical problems of overdetermination of the solution, the solution is to provide a separate part of the frame that is only stiff in a limited direction, as proposed in US-A-6 529 264. To make them, and then connect them after the two barrels are positioned relative to each other through the assembly frame. In addition, thermodynamic problems of overdetermined assembly are to make the material of the frame portions and the assembly frame portion the same, as also proposed in US-A-6 529 264.

It is an object of the present invention to solve the problems associated with the supply of conventional reference frame materials, without causing performance problems.

According to the invention,

An illumination system providing a projection beam of radiation;

A support structure for supporting patterning means, the patterning means serving to impart a pattern to the cross section of the projection beam;

A substrate table for holding a substrate;

A projection system for projecting the patterned beam onto a target portion of the substrate; And

An isolated reference frame providing a reference plane on which the substrate is measured,

A lithographic apparatus is provided wherein the reference frame comprises a material having a high coefficient of thermal expansion.

By providing a reference frame comprising a material having a high coefficient of thermal expansion, a wider range of materials can be used for the reference frame. Materials such as aluminum and aluminum alloy materials have been found to reduce significant product costs and significantly reduce lead-times. In addition, the present invention provides a surprising additional effect that the dynamic performance of the reference frame is equal to or better than the reference frame made of conventional materials such as Invar. By rejecting the assumption that the reference frame should be made of a material having a low coefficient of thermal expansion in order to achieve the required thermal and thermodynamic performance, the inventors have overcome substantial technical biases.

In a preferred embodiment, the reference frame supports the measuring system and measuring means for determining a particular dimension of the substrate prior to exposure.

In a preferred embodiment, the coefficient of thermal expansion is greater than approximately 2.9 × 10 ⁻⁶ / K. Surprisingly, materials with coefficients of thermal expansion greater than approximately 2.9 × 10 ⁻⁶ / K provide a reference frame with sufficient mechanical and thermal stability. It has been found that SiSiC having a coefficient of thermal expansion of approximately 2.9 × 10 ⁻⁶ / K is a material that meets these requirements.

In a preferred embodiment, the reference frame is for example a composite, sandwiched or laminated structure of aluminum, aluminum alloy, titanium, iron, cast-iron, steel, stainless steel, copper, ceramic material, concrete, granite, porcelain ( porcelain) material or combinations of these materials. By using these materials, the manufacturing cost of the reference frame is reduced. Furthermore, the degree of freedom of design is increased. The use of more versatile materials results in less technical manufacturing documentation with less change in the design of the reference frame and less mechanical development required for the new frame design. In particular, aluminum or aluminum alloys, for example, are particularly kinetically robust.

In a preferred embodiment, the reference frame comprises a solid block of material. By providing a reference frame in the form of a solid block, the manufacturability of the reference substrate is further improved in contrast to conventional reference substrates, which may include a large number of casting or plate portions that require welding together. Solid blocks also provide low internal thermal resistance and high thermal capacity. This results in only a very small change in temperature from changes in dynamic heat load, resulting in only a small thermal drift of the reference frame. In a preferred embodiment, the solid block is machined to form the reference frame. By machining the solid block, time consuming and expensive welding procedures can be avoided.

In a preferred embodiment, the reference frame is provided with a thermal conditioning system for controlling the temperature of the projection system with respect to the reference frame. By providing such a thermal conditioning system, the long term thermal stability of the reference frame is improved. In addition, after thermal drift of the reference frame and optical system (eg caused by service, maintenance and installation, etc.), thermal stabilization to reach the required performance is significantly reduced by active cooling. Another advantage is the improved thermal conditioning of the projection system in which a actively conditioned reference frame is provided.

In a preferred embodiment, the reference frame is provided with a highly infrared reflective surface. By providing the highly infrared reflective surface in the reference frame, the risk of contamination can be reduced, and / or the infrared reflection can be increased, and / or the coefficient of friction can be increased. In particular, the reflective surface can be provided in the form of a metallic material coating, for example of nickel.

In a preferred embodiment, the reference frame is made of a material having high specific heat and / or high thermal conductivity. In particular, certain materials have a specific heat higher than approximately 600 J (KgK) and / or a thermal conducting phase higher than approximately 20 W (m K).

By providing a reference frame of material with high specific heat and / or high thermal conductivity, the thermal stability of the frame is improved. In one embodiment, the reference frame is provided with a first temperature sensor for sensing the temperature of the reference frame.

In a further embodiment, the projection system comprises a projection lens, wherein the projection lens is provided with a second temperature sensor for sensing the temperature of the projection lens.

A further embodiment includes a thermal conditioning system for thermally conditioning at least one of the reference frame and the projection system based on the temperature sensed by at least one of the first and second temperature sensors. In this way, short and long term temperature fluctuations can be compensated.

In a further embodiment, the thermal conditioning system includes a control circuit, a temperature regulating element, and a heat transfer system that control the amount of heat transferred to or from at least one of the reference frame and the projection lens. An adjusting element regulates the amount of heat transferred by the heat transfer system, wherein the heat transfer system is in thermal contact with at least one of the reference frame and the projection lens to transfer heat to or from at least one of the reference frame and the projection lens. And the control circuit is arranged to respond to a temperature sensed by at least one of the first and second temperature sensors, the temperature regulating element responsive to the control circuit and in thermal contact with the heat transfer system. The set temperature is reached in at least one of the frame and the projection lens. In this way, temperature control of at least one of the reference frame and the projection lens is improved.

In a further embodiment, the control circuit is arranged to compensate for short-term environmental temperature variations in view of the temperature sensed by the first temperature sensor. In this way the thermal stability of the device is improved.

In a further embodiment, the control circuit is arranged to compensate for long term environmental temperature fluctuations in view of the temperature sensed by the second temperature sensor. In this way, the thermal stability of the device is improved.

In a further embodiment, the thermal conditioning system includes a single control loop that controls the temperature of the reference frame and the projection lens. In this way, long term and short term environmental temperature fluctuations can be considered without significantly adding to the complexity and cost of the device.

In a further embodiment, the heat transfer system includes a conditioning fluid that is heated or cooled to the set temperature. In this way, the thermal conditioning system provides various and effective device temperature controls.

According to a further aspect of the invention,

Providing a substrate;

Providing a projection beam of radiation using an illumination system;

Imparting a pattern to the cross section of the projection beam using patterning means; And

Projecting the patterned radiation beam onto a target portion of the substrate;

Providing an reference plane on which the substrate is measured with respect to an isolated reference frame,

The reference frame is provided with a device manufacturing method, characterized in that it comprises a material having a high coefficient of thermal expansion.

Although reference is made to the use of lithographic apparatus in the manufacture of ICs, such devices are used to fabricate guidance and detection patterns for the manufacture of integrated optical systems, magnetic domain memories, liquid crystal display panels (LCDs), thin film magnetic heads, and the like. It will be appreciated that there are other applications such as Those skilled in the art will appreciate that with respect to these alternative applications, terms such as "wafer" or "die" as used herein will be considered synonymous with more general terms such as "substrate" or "target portion", respectively. have. The substrate referred to herein may be processed, for example, before or after exposure in a track (a tool that typically applies a layer of resist to the substrate and develops the exposed resist) or a metrology or inspection tool. Where applicable, the disclosure herein may be applied to the above and other substrate processing tools. In addition, the substrate may be processed one or more times, for example to produce a multilayer IC, so that the term substrate used herein may refer to a substrate that already includes a multi-treated layer.

As used herein, the terms "radiation" and "beam" refer to ultraviolet (UV) rays (e.g., 365, 248, 193, 157 or 126 nm) and extreme ultraviolet (EUV) rays (e.g., wavelengths). In the range from 5 to 20 nm) and particle beams such as ion beams or electron beams.

As used herein, the term "patterning means" should be broadly interpreted as referring to a means that can be used to impart a pattern to a cross section of a projection beam, such as to create a pattern in a target portion of a substrate. It should be noted that the pattern imparted to the projection beam does not exactly correspond to the desired pattern of the substrate target portion. In general, the pattern imparted to the projection beam will correspond to a particular functional layer in the device to be formed in the target portion, such as an integrated circuit.

The patterning means can be transmissive or reflective. Examples of patterning means include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography and include mask types such as binary, alternating phase-shift, and attenuated phase-shift and various hybrid mask types. An example of a programmable mirror array is a matrix arrangement of small mirrors, each of which is individually tilted to reflect the incident beam of radiation in different directions; In this way, the reflected beam is patterned. In each example of the patterning means, the support structure can be a frame or a table, for example, which can be fixed or movable as required and can ensure that the patterning means is in a desired position with respect to the projection system, for example. Any use of the term "reticle" or "mask" as used herein may be considered synonymous with the more general term "patterning means".

As used herein, the term "projection system" refers to refractive optics, as appropriate for the exposure radiation used, or for other factors such as the use of immersion fluid or the use of a vacuum. It should be broadly interpreted as encompassing various types of projection systems including systems, reflective optical systems and catadioptric optical systems. Any use of the term "lens" herein may be considered as synonymous with the more general term "projection system".

In addition, the illumination system may encompass various types of optical components, including refractive, reflective and catadioptric optical components for directing, shaping or controlling the projection beam of radiation, which will be described later in the description. May be referred to individually or individually as a "lens."

The lithographic apparatus may be of a type having two (dual stage) or more substrate tables (and / or two or more mask tables). In such "multiple stage" machines the additional tables may be used in parallel, or preparatory steps may be carried out on one or more tables while one or more other tables are being used for exposure.

The lithographic apparatus may also be of the type in which the substrate is immersed in a liquid, for example water, having a relatively high refractive index to fill the space between the final element of the projection system and the substrate. Immersion liquids may be applied to other spaces in the lithographic apparatus, for example, between the mask and the first element of the projection system. Immersion techniques are well known in the art for increasing the numerical aperture of projection systems.

1 schematically depicts a lithographic projection apparatus according to a particular embodiment of the invention. The device is:

An illumination system (illuminator) IL for supplying a projection beam PB of radiation (for example UV or EUV radiation);

A first support structure (e.g. a mask table) which supports the patterning means MA (e.g. a mask) and is connected to the first positioning means PM which accurately positions the patterning means with respect to the item PL. MT);

A substrate table (e.g. wafer table) WT, which is held by the substrate W (e.g. a resist coated wafer) and connected to second positioning means PW for accurately positioning the substrate with respect to the item PL. ); And

A projection system for imaging the pattern imparted to the projection beam PB by the patterning means MA onto the target portion C (eg comprising at least one die) of the substrate W ( PL) (e.g., refractive projection lens).

As shown, the device is transmissive (e.g., employing a transmissive mask). Alternatively, the device may be reflective (e.g., employing some form of programmable mirror array as described above).

The illuminator IL receives the radiation beam from the radiation source SO. The radiation source and the lithographic apparatus can be separate objects, for example when the radiation source is an excimer laser. In such a case, the radiation source cannot be seen to form part of a lithographic apparatus, and the radiation beam is provided with a radiation source SO with the aid of a beam delivery system BD, for example comprising a suitable directing mirror and / or beam expander. ) Is passed through the illuminator (IL). In other cases, for example, if the radiation source is a mercury lamp, the radiation source may be an integral part of the device. The radiation source SO and the illuminator IL may be referred to as a radiation system together with the beam delivery system BD if necessary.

The illuminator IL may include adjusting means AM for adjusting the angular intensity distribution of the beam. In general, at least the outer and / or inner radial sizes (commonly referred to as -outer and -inner, respectively) of the intensity distribution in the pupil plane of the illuminator can be adjusted. In addition, the illuminator IL generally includes various other components such as an integrator IN and a capacitor CO. The illuminator provides a conditioned radiation beam called projection beam PB, which has a uniformity and intensity distribution in its cross section.

The projection beam PB is incident on the mask MA, which is held on the mask table MT. The projection beam PB across the mask MA passes through the lens PL, which focuses the beam PB on the target portion C of the substrate W. By the second positioning means PW and the position sensor IF2 (e.g., interferometer device), the substrate table WT positions the different target portions C in the path of the beam PB, for example. Can be precisely moved. Similarly, the first positioning means PM and another position sensor (not clearly shown in FIG. 1) are the paths of the beams PB, for example after mechanical retrieval from the mask library or during scanning. It can be used to accurately position the mask MA with respect to. In general, the movement of the objective tables MT and WT is characterized by a long stroke module (coarse positioning) and a short stroke module (fine positioning) forming part of the positioning means PM and PW. Will be realized with the help of However, in the case of a stepper (as opposed to a scanner), the mask table MT may be connected to only a short stroke actuator or may be fixed. The mask MA and the substrate W may be aligned using the mask alignment marks M1 and M2 and the substrate alignment marks P1 and P2.

The device shown can be used in the following preferred modes.

1. In the step mode, the mask table MT and the substrate table WT are basically kept stationary, while the entire pattern imparted to the projection beam is placed on the target portion C at once (i.e., a single static exposure). Projected. Subsequently, the substrate table WT is shifted in the X and / or Y direction so that another target portion C may be exposed. In the step mode, the maximum size of the exposure field limits the size of the target portion C to be drawn during a single static exposure.

2. In the scan mode, the mask table MT and the substrate table WT are simultaneously scanned while the pattern imparted to the projection beam is projected onto a predetermined target portion C (ie, a single dynamic exposure). The speed and direction of the substrate table WT relative to the mask table MT are determined by the (de-) magnification and image reversal characteristics of the projection system PL. In the scan mode, the maximum size of the exposure field limits the width (in the unscanned direction) of the target portion during a single dynamic exposure, while the length of the scanning operation determines the height (in the scanning direction) of the target portion.

3. In another mode, the mask table MT holds the programmable patterning means and remains essentially static, while the substrate table WT while the pattern imparted to the projection beam is projected onto the target portion C. ) Is moved or scanned. In this mode, a pulsed radiation source is generally employed, and the programmable patterning means is updated as needed after every movement of the substrate table WT or between successive radiation pulses during scanning. This mode of operation can be readily applied to maskless lithography utilizing programmable patterning means, such as a programmable mirror array of the kind mentioned above.

In addition, combinations and / or variations of the modes of use described above, or entirely different modes of use may be employed.

Also shown in FIG. 1 are two frames: a reference frame MF and a base frame BF, also known as "metrology" frames. The reference frame MF provides a reference plane against which the wafer is measured and is mechanically isolated from the main device structure. Typically, the reference frame MF is isolated dynamically or thermodynamically. In particular, the reference frame MF is independent of the base frame BF shown in FIG. 1. The reference frame MF supports sensitive components such as interferometer IF and other position sensors. In addition, depending on the particular lithographic apparatus, the reference frame may support the projection system PL. The reference frame also isolates the components supported thereon from vibration. The reference frame MF also supports a metrology system such as interferometer IF and optionally the projection system PL, while the base frame supports other components. In particular, the base frame BF supports the vibration isolation system VI which mechanically isolates the reference frame MF from the main device structure. Additionally and optionally, other components, such as wafer stage WT (not shown in FIG. 1) and reticle stage MT, including a long stroke motor, may be supported. In one embodiment, the base frame BF is in contact with the manufacturing floor and may alternatively not. The vibration isolation system VI may have a low modulus of elasticity in the elastic support for the reference frame MF, for example an airmount or other equivalent system such as a magnetic system, a mechanical system comprising low rigidity mechanical beams. It may also be realized as a fluid-based system that provides. In a preferred embodiment, the vibration isolation system is arranged between the base frame BF and the reference frame RF. It should be noted that the airmount is suitable for use in lithographic apparatus operating under vacuum or atmospheric conditions.

The reference frame MF may be realized, for example, as a heavy table. According to the invention, the reference frame MF is made of a material having a high coefficient of thermal expansion. Such materials may include aluminum, aluminum alloys, titanium, irons, cast-irons, steels, stainless steels, copper, ceramic materials, concrete, granite, porcelain or combinations of these materials in composite, sandwiched or laminated structures. May be, but is not limited to these.

Table 1 shows some typical properties of some suitable construction materials. In addition, the values of the same properties for the conventional material Invar have been presented to aid the comparison.

material Coefficient of Thermal Expansion (x10 ^-6 / K) Specific heat (J / (kg K)) Thermal Conductivity (W / (m K)) Mass density (kg / m ³ ) Modulus of elasticity (N / mm ² ) Invar (traditional) 1.5 500 13 8030 140000 Aluminum alloy (for example, AA5083 O) 24 900 120 2660 71000 Steel (for example, Fe 360) 12 460 57 7850 210000 Stainless steel (for example, 304 (L) or 316 (L)) 16 500 16 7900 210000 Cast iron (for example, GJS400-15) 12 500 35 7100 170000 Copper 17 390 390 8900 120000 Ceramic materials (eg SiSiC) 3 700 170 2950 410000 Porcelain 2400 800 5 2400 104000 granite 2650 820 3.5 2650 30000

It should be noted that aluminum alloys typically have a coefficient of thermal expansion in the region of 23 to 24.5 × 10 ⁻⁶ / K or near.

The reference frame MF is made from a monolithic part, ie a solid block. It may be cast or machined from one block.

It has been found that the reference frame MF made from aluminum in this way has a mass approximately equal to the conventional reference frame, for example. Thus, its integration into the lithographic apparatus, in particular its interface with the vibration isolation system, can be achieved very easily. Surprisingly, the temperature environment around the reference frame also causes an expected 2 nanometer drift over 5 meters over a few minutes, such that a conventional reference frame material such as Invar with a much lower coefficient of thermal expansion than the materials considered in accordance with the present invention. It has been found to be stable enough to match the tolerance achieved by them. Contrary to expectations, the dynamic performance of reference frames made from materials that are expected to exhibit poor dynamic performance due to their high coefficient of thermal expansion has been found to exhibit dynamic performance within the tolerances required in conventional lithographic apparatus. In addition, the center of gravity can be easily adapted without significant impact on dynamic performance. In one alternative embodiment, a reference frame MF is provided that is heavier than conventional reference frames. This is achieved, for example, by increasing its dimensions and / or selecting a material such as iron with a higher density. Although this heavier reference frame requires recalibration of the vibration isolation system VI, it provides an additional advantage that the dynamic performance of the reference frame MF is improved. One suitable material is an aluminum alloy of type AA5083 (Al-4.4Mg-07Mn-0.15Cr). With regard to AA5083 or similar alloys, it should be noted that it has the advantage of having very low thermal stress levels. This offers several advantages in terms of machining the block of material to form the reference frame MF and in terms of the long term stability of the reference frame.

In addition, it should be understood that other aluminum based alloys may also be used. With regard to specific heat and thermal conductivity, it has been found that the specific heat is preferably higher than approximately 600 J (kgK) and the thermal conductivity is preferably greater than approximately 20 W / (m K).

Optionally, a cooling system may be employed in or in connection with the reference frame MF in order to improve thermal stability. A fluid cooling system such as water or air cooling may be used to cool the reference structure. According to the embodiments in which the projection system PL is supported by the reference frame MF, a cooling system may be optimized for or in connection with the reference frame in addition to cooling the projection system. In particular, the cooling system provides long-term stability and short recovery times after thermal drift (eg, as experienced after service, maintenance, installation, etc.).

2 is a detailed view of a lithographic apparatus according to a further embodiment of the present invention. In particular, FIG. 2 shows a reference frame MF suitable for use in a TwinScan lithographic apparatus. The twinscan device allows the measurement at the measurement station 2 of one substrate W1 prior to the exposure while the exposure at the exposure station 4 of the other substrate W2 is performed. While the substrate W1 is in the measuring station 2, at the exposure stage, a first interferometer IF1 comprising a first Z-mirror ZM1 is provided to compensate for distortion at the substrate surface to provide a "substrate map" of the substrate. In order to produce the contours, i.e., interferometer IF1 maps the contour of the substrate surface. While the substrate W2 is in the exposure station 4, the second interferometer IF2 including the second Z-mirror ZM2 faithfully has the "substrate map" generated in the reference frame MF with respect to the substrate W2. To be regenerated. In this particular embodiment, the reference frame MF supports both the metrology system IF and the projection system PL. In a particular lithographic apparatus, the reference frame MF includes a first reference frame portion on which components that provide a measurement function are mounted and a second reference frame portion on which components that provide an exposure measurement function are mounted. Typically the two frame parts are mounted, for example, by bolting against each other or against an additional mounting frame. In embodiments where the reference frame includes one or more frame portions, each frame portion may be provided with its own vibration isolation system, respectively. Alternatively, a single vibration isolation system may be provided. 2 also shows an example of a thermal conditioning system WC, for example a cooling system, in particular a water cooling system WC formed in the reference frame MF. As shown, the reference frame MF is provided with ducts in the frame structure through which the coolant flows into the frame structure through the inlet 6 and through which the coolant leaves the structure. The ducts are formed to provide circulating cooling around the portions of the reference frame MF, which are arranged opposite the measuring station 2 and the exposure station 4, respectively. The cooling system includes one or more cooling circuits. In the particular embodiment shown in FIG. 2, two cooling ducts are provided. In alternative embodiments, cooling by one cooling circuit may be provided. In certain embodiments, a single cooling circuit may provide cooling fluid to both the projection lens PL and the reference frame MF. The remaining components shown in FIG. 2 correspond to those shown in FIG. 1 and described in connection with it, and thus further description thereof will be omitted.

3 shows a top view of a reference frame isolated from a base frame according to an embodiment of the present invention showing particular components supported on the reference frame MF. In particular, FIG. 3 illustrates in more detail the isolation relationship between the reference frame MF and the base frame BF, and also illustrates the reference frame MF and the components mounted thereon in more detail.

In the embodiment shown in FIG. 3, the reference frame MF comprises a first part 3 and a second part 5, wherein the first part and the second part are machined from the first and second blocks, respectively. Processed. Alternatively, they may be cast. The first and second portions 3 and 5 cooperate with each other to form a reference frame MF. In particular, the first part serves to support the components, among others, for performing the measuring stage and the exposure stage. For example, it supports components such as the projection lens PL, a level sensor module LS for sensing the level of the substrate at the measurement position, and an alignment module AL for evaluating the alignment of the substrate at the measurement position. Other components may be mounted on the bottom side of the reference frame MF. These are described and illustrated with reference to FIG. 4. In the embodiment shown in FIG. 3, the second part 5 supports a vibration isolation system VI which serves to isolate the reference frame MF from the base frame BF. It is in the form of a bridge, in which bridge supports 7, 8 are arranged on the first part 3. The portion 10 extending the length of the bridge is supported by bridge supports 7, 8. At opposite ends 9 of the extension 10 there is a vibration isolation system support 9. In FIG. 3 the air mount AM forming the vibration isolation system VI is arranged between the part 9 and the base frame BF. Through the bridge 5, the isolation of the vibrations from the base frame BF given by the air mount AM is transferred to the components mounted on the first part 3. In the embodiment shown in FIG. 3, three air mounts are provided: one at each end of the bridge portion and one at both ends of the bridge portion and at the ends opposite to the longitudinal direction of the first part of the reference frame MF and the base frame. A third one (not shown in FIG. 3 but shown in FIG. 4) is disposed between the BFs. However, it is to be understood that the present invention is not limited to this form only, and that the vibration isolation system VI may be realized in a number of alternative ways with regard to both the nature of the system and the number and arrangement of system components. In an alternative embodiment to that shown in FIG. 3, the reference frame MF consists of a single part, wherein the functions described above with respect to the first and second parts are combined into a single part.

In addition, the reference frame shown in FIG. 3 has a highly infrared reflecting surface CO. FIG. This may be realized by applying a coating to at least a portion of the reference frame outer surface. The coating covers the surface of the reference frame. It may cover at least part surface of the reference frame MF. The coating is made of a metallic material such as nickel. Alternatively, the highly infrared reflecting surface may be formed by polishing or surface treatment of the reference frame MF.

4 shows a bottom view of the reference frame MF isolated from the base frame BF as shown in FIG. 3. In particular, the components mounted on the lower side of the reference frame are shown. These include an interferometer IF1 arranged to play roles at the measurement station 2 and an interferometer IF2 arranged to perform roles at the exposure station 4. In relation to each of these interferometers IF1, IF2, respective Z-mirrors ZM1, ZM2 are associated. Also shown is a substrate chuck SC that serves to support the substrate W at the measurement station 2. After the measuring station is performed, the substrate chuck SC moves from the aligned position by the measuring station 2 to the aligned position with respect to the exposure station 4. As mentioned above, in one embodiment, two substrate chucks are provided in which each substrate is provided. The chucks are positioned and moved relative to one another so that the first substrate can be measured at the measurement station 2 while the second substrate is exposed at the exposure station 4. This arrangement increases the throughput of the substrates throughout the lithographic apparatus.

4 also shows a reference frame MF for the base frame BF, with an additional air mount AM provided between the base frame BF and a portion of the first part 3 of the reference frame MF. Shows vibration isolation. Also, one of the air mounts AM mounted between the second part 5 and the base frame BF can be seen.

The temperature control of the projection lens PL, the reference frame MF, the interferometer IF and other sensors is preferably carried out below mK (milliKelvin). For the reference frame MF made of a material such as aluminum, the temperature control is preferably performed at about 0.1 mK / 5 minutes. In addition, the temperature stability of the environment of the projection lens PL, the reference frame MF, the interferometer IF and other sensors is preferably within about 30 mK. It has been found that conventional lithographic apparatus does not provide such temperature control.

In conventional lithographic apparatus, a temperature sensor is provided only in connection with the projection system. Determining the temperature set point for the thermal conditioning system for the supply of water to the lens circuit water cabinet (LCWC) and motor circuit water cabinet (MCWC) and the air to the air control cabinet (ACC) Only sensors are used. Due to the large time constant and thermal isolation of the lens, the lenses have been found to be sensitive to environmental temperature fluctuations. On the other hand, the reference frame MF and other temperature critical components are much more sensitive. Thus, by sensing the temperature of the reference frame MF and the projection lenses, both long term and short term variations can be detected and compensated for. In one embodiment of the present invention, the reference frame MF of a material, such as aluminum, having a high coefficient of thermal expansion can be thermally conditioned, for example using a water conditioning system. In a further embodiment, the reference frame MF is conditioned using the same water conditioning the projection system, in particular the projection lens. Since the reference frame MF is more sensitive to environmental temperature fluctuations than the conventional reference frame, in order to compensate for short-term environmental temperature fluctuations, for example, the opening and closing of the cover or the influence of the actuator, the temperature of the reference frame MF Is sensed and the sensed temperature is preferably used in a temperature control algorithm for compensation of short term environmental temperature fluctuations. In a further embodiment, a control algorithm for the compensation of long-term environmental temperature fluctuations in which the temperature of the projection system PL is sensed, for example by a sensor disposed on the projection lens and the sensed temperature is combined with the temperature of the reference frame. It is preferably used for. In particular, since the temperature of the projection system is preferably kept stable at the operating temperature, it is desirable to control the long term temperature of the apparatus. Typical operating temperatures are around 22 ° C. As will be described in more detail below, it has been found that both long and short temperature variations can be controlled in a single control loop.

5 is a detailed view of the reference frame MF, the projection lens PL and the thermal conditioning system 20. In particular, by controlling the temperatures of the reference frame MF and the projection lens PL, the thermal stability of the lithographic apparatus is improved. In particular, by controlling the temperature of the reference frame having a high coefficient of thermal expansion made of a material such as aluminum, the thermal stability of the frame is improved. The reference frame MF made of aluminum is more sensitive to environmental temperature fluctuations than conventional reference frames made of Invar.

In FIG. 5, the control loop is used to adjust the temperature of at least one of the projection lens PL and the reference frame MF. In this embodiment, at least one first temperature sensor 21 is provided for sensing the temperature of the reference frame MF. An additional second temperature sensor 22 may be provided on the projection lens PL to sense the temperature of the projection lens PL. The temperature sensors may include a device whose resistance is temperature dependent. In order to control the temperature of at least one of the reference frame MF and the projection system PL based on the temperatures sensed by at least one of the first and second temperature sensors 21, 22, the thermal conditioning system 20. This is provided. In one embodiment, the temperature of the reference frame MF and the projection lens PL is controlled based on the temperatures sensed by both the first and second temperature sensors 21, 22. The thermal conditioning system 20 includes a control circuit 24 for controlling the amount of heat transferred to or from one or more of the reference frame MF and the projection lens PL. Also provided is a temperature regulation element 26. The temperature regulation element 26 is arranged to heat and / or cool the fluid conveyed in the heat transfer system. The control circuit 24 is arranged between the temperature sensors 21, 22 and the temperature regulating element. The control circuit 24 is arranged to adjust the amount of heating so that the sensed temperature is adjusted towards the set temperature. The control circuit 24 provides a predetermined control signal to the temperature regulation element 26 to control the heater and / or the cooler in accordance with the control signal. Thermal conditioning system 20 further includes heat transfer systems 28, 30, 32, 34, 36, 38. The temperature regulating element 26 is arranged in thermal contact with the heat transfer systems 28, 30, 32, 34, 36, 38. The temperature control system 26 regulates the amount of heat transferred by the heat transfer systems 28, 30, 32, 34, 36, 38. Further, the heat transfer system 28, 30, 32, 34, 36, 38 may be adapted to transfer heat to or from one or more of the reference frame MF and the projection lens PL. It is arranged in thermal contact with at least one of the projection lenses PL. In particular, the heat transfer system 28, 30, 32, 34, 36, 38 is a supply duct 28, 36, 38 for supplying the conditioning medium 34 to the reference frame MF and the projection lens PL. ). The conditioning medium may be a fluid such as water. The supply ducts 28, 36, 38 are arranged to extend through portions of the reference frame MF and the projection lens PL. In particular, the supply duct 38 includes an enclosed channel formed in the reference frame MF, and the supply duct 36 defines an enclosed channel formed in the projection lens or projection system PL. Include. The enclosure channels 36 and 38 are arranged to extend in the reference frame MF and the projection system PL so that they do not affect the function of these components. The supply ducts 28, 36, 38 are provided with a circulation pump 30. In addition to or alternatively to the cooling element of the temperature control system 26, a cooling element (not shown) may be provided upstream of the temperature control system 26 arranged to remove excessive heat from the conditioning medium 34. have. In FIG. 5, one first and second temperature sensor 21, 22 is shown. In a further embodiment, a plurality of first temperature sensors and a plurality of second temperature sensors are provided. In this case, the average control circuit determines and adjusts the average sensed temperature. The conditioning medium 34 may be cooled by an adjusted amount instead of being heated. In FIG. 5 the conditioning medium 34 flows sequentially through the reference frame MF and the projection lens PL, and in an alternative embodiment this flow is parallel towards the reference frame MF and the projection lens PL. You may. In alternative embodiments, the flow rate of the conditioning medium 34 may be adjusted to control the heat transferred by the heat transfer system. In a further alternative embodiment, in addition to the closed supply duct 28 as shown in FIG. 5, the supply duct 28 may comprise an open pipe into which a new conditioning medium is introduced. The heat transfer system does not have to have a conditioning medium circulated through the system.

In particular, the control circuit 24 is arranged to respond to a temperature sensed by at least one of the first and second temperature sensors 21, 22, and the temperature regulating element 26 responds to the control circuit 24. The thermal contact with the heat transfer systems 28, 30, 32, 34, 36, 38 causes the set temperature to be reached in at least one of the reference frame MF and the projection lens PL. In a further particular embodiment, the control circuit 20 is arranged to take the temperature sensed by the first temperature sensor 21 in consideration of compensating for short-term environmental temperature fluctuations. In this way, short-term temperature fluctuations such as opening and closing of the cover, effect of the actuator can be compensated for. In particular, short-term environmental temperature effects on the reference frame can be compensated for to prevent short-term thermal drift of the frame and sensors. In a further embodiment, the control circuit 20 is arranged to take the temperature sensed by the second temperature sensor 22 in consideration of compensating for long term environmental temperature fluctuations. In this way, since the projection lens PL is preferably kept at a constant reference temperature, in particular, the temperature of the projection lens PL is kept at a constant temperature. In particular, the lenses may be maintained at a reference temperature of 22 ° C., for example. In one embodiment, compensation for short and long term fluctuations occurs in a single control loop. In a further embodiment, the heat transfer systems 28, 30, 32, 34, 36, 38 transfer heat to or from the reference frame MF and the projection lens PL. In this way, both the reference frame MF and the projection lens PL are kept at a predetermined temperature without substantially increasing the complexity of the control of the lithographic apparatus. In one embodiment, a gas supply, such as an air shower, provides gas to a location between the projection system PL and the substrate W, wherein the temperature of the gas supplied to the location is determined by the temperature of the conditioning fluid. . Since the temperature of the air shower is determined by the lens cooling water supplied by the supply duct 36, a more thermally stable overall system is obtained.

6 to 8 show the results obtained according to one embodiment of the invention. 6 to 8, trace 60 is the temperature of the lens (CtLnsTempFM), trace 61 is the temperature of the set point of the lens coolant (CtLcsSept), trace 62 is the reference frame random temperature (CtMfMeasTemp) at the measurement side, and trace 63 Is the temperature of the reference frame at the exposure side CtMfExpTemp.

FIG. 6 shows experimental results obtained according to an embodiment of the present invention in which the reference frame MF is aluminum. In particular, in FIG. 6, the temperature is recovered using the lens sensor 22, and the reference frame MF sensor 21 is used when the substrate W is exposed. It can be seen that the long term drift of the lens PL is not corrected by this method. In a preferred embodiment, both the sensor 21 sensing the temperature of the reference frame MF and the sensor 22 sensing the temperature of the projection lens PL prevent the long-term lens temperature drift observed in FIG. 6. Used in control algorithms to

FIG. 7 shows the results shown in FIG. 6 in detail. In particular, FIG. 7 shows the results near the exposure phase. A correction for short term experimental drift can be seen. In the vicinity of 20.00 h, exposure began, resulting in an increase in environmental temperature of approximately 20 mK, which resulted in a decrease in temperature of the LCW setpoint. At around 10.00h, the cover is removed from the electronic cabinets, causing a sudden reduction in environmental air. This is calculated by control by a sudden temperature increase of the setpoint. As shown in FIG. 7, it can be seen that the temperature of the reference frame MF is kept stable.

8 shows the results shown in FIG. 6 in detail. In particular, FIG. 8 shows experimental results zoomed in at a reference frame (MF) temperature. It can be seen that at all times the temperature fluctuation is about 0.1 mK, which corresponds to a measurement error of 1 nm except when the cover is removed. Removal of the cover can be considered an exceptional situation. Even at this time, the results shown in FIG. 8 indicate that the recovery for this action is very rapid.

While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. The description is not intended to limit the invention.

According to the present invention, it is possible to solve the problems associated with the supply of conventional reference frame materials with little effect on performance.

Claims (28)

In a lithographic apparatus, An illumination system providing a projection beam of radiation; A support structure for supporting patterning means, the patterning means serving to impart a pattern to the cross section of the projection beam; A substrate table for holding a substrate; A projection system for projecting the patterned beam onto a target portion of the substrate; And An isolated reference frame providing a reference plane on which the substrate is measured, A lithographic apparatus according to claim 1, wherein the reference frame comprises a material having a high coefficient of thermal expansion. The method of claim 1, And said reference frame supports a measurement system for determining particular dimensions of said substrate prior to its exposure. The method of claim 1, And the frame of reference supports the projection system. The method of claim 1, Wherein said coefficient of thermal expansion is greater than approximately 2.9 × 10 ⁻⁶ / K. The method of claim 1, The reference frame may be a composite, sandwiched or laminated structure of aluminum, aluminum alloy, titanium, iron, cast-iron, steel, stainless steel, copper, ceramic material, concrete, granite, porcelain material or a combination of these materials. A lithographic apparatus comprising one of the combinations. The method according to any one of claims 1 to 5, And said frame of reference comprises a solid block of material. The method of claim 6, And said solid block is machined to form said reference frame. The method of claim 7, wherein The reference frame includes a first portion for supporting a component for performing the measuring stage and the exposure stage, and a second portion for supporting a vibration isolation system that serves to isolate the reference frame from a base frame. Lithographic apparatus. The method according to any one of claims 1 to 5, And the reference frame is provided with a thermal conditioning system for controlling the temperature of the projection system with respect to the reference frame. The method of claim 9, And the thermal conditioning system uses the conditioning fluid to condition the reference frame and the projection lens. The method according to any one of claims 1 to 5, The reference frame is provided with a highly infrared reflective surface. The method of claim 11, And said face is provided by a metal coating such as nickel. The method according to any one of claims 1 to 5, And said reference frame is made of a material having high specific heat and / or high thermal conductivity. The method of claim 13, And the specific heat is greater than approximately 600 J (kgK) and the thermal conductivity is greater than approximately 20 W / (m K). delete The method of claim 8, The apparatus further comprises a base frame for supporting the vibration isolation system. The method according to any one of claims 1 to 5, And the reference frame is provided with a first temperature sensor for sensing a temperature of the reference frame. The method of claim 17, And said projection system comprises a projection lens, said projection lens being provided with a second temperature sensor for sensing a temperature of said projection lens. The method of claim 18, And a thermal conditioning system for thermally conditioning at least one of said reference frame and said projection system based on a temperature sensed by at least one of said first and second temperature sensors. . The method of claim 19, The thermal conditioning system includes a control circuit, a temperature control element and a heat transfer system for controlling the amount of heat transferred to or from at least one of the reference frame and the projection lens, wherein the temperature control element is controlled by the heat transfer system. Adjusting the amount of heat transferred, wherein the heat transfer system is in thermal contact with at least one of the reference frame and the projection lens to transfer heat to or from one of the reference frame and the projection lens, and the control circuit Arranged to respond to a temperature sensed by at least one of the first and second temperature sensors, wherein the temperature regulating element is responsive to the control circuit and in thermal contact with the heat transfer system to the reference frame and the projection lens. A lithographic field characterized in that at least one of the set temperatures is reached. Chi. The method of claim 20, And said control circuit is arranged to take into account the temperature sensed by said first temperature sensor in compensating for short-term environmental temperature fluctuations. The method of claim 20, And said control circuit is arranged to take into account the temperature sensed by said second temperature sensor to compensate for long term environmental temperature fluctuations. The method of claim 20, And the heat transfer system transfers heat to or from the reference frame and the projection lens. The method of claim 20, And said thermal conditioning system comprises a single control loop for controlling the temperature of said reference frame and said projection lens. The method of claim 20, And said heat transfer system comprises a conditioning fluid heated or cooled to said set temperature. The method of claim 25, And a gas supply for providing gas to a position between the projection system and the substrate, wherein the temperature of the gas supplied to the position is determined by the temperature of the conditioning fluid. A frame of reference according to any of the preceding claims. In the device manufacturing method, Providing a substrate; Providing a projection beam of radiation using an illumination system; Imparting a pattern to the cross section of the projection beam using patterning means; Projecting the patterned radiation beam onto a target portion of the substrate; Using an isolated reference frame to provide a reference plane against which the substrate is measured, Wherein said reference frame comprises a material having a high coefficient of thermal expansion.

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